In here you'll find links to various sites all with something worthwhile to say about tactics.
Some of the links take you to pages where you can click through to more information, rather than linking to each page, I've linked to the main page of such sites.
Dog Fighting handbook
This is the DF sim bible. Although it was written with European Air War in mind, its still packed full of useful info.
http://www.simhq.com/_air/PDF/STK_EAW_v106.pdf
This is a great site with superb diagrams of CFM (Combat Flight Manouvers). The guy who wrote it is talking about jets, but the principles apply to prop planes too.
http://www.combataircraft.com/intel/tactics/
This site has it all... Make sure you have a really good look around. The site is well thought out and its easy to find everything you need there.
http://www.musketeers.org/training.htm
This is a great site with IL2 specific gunnery tips, very handy.
http://12iapil2ops.0catch.com/saku_gunnery_tips.htm
This is another site with loads of CFM stuff, but there's a load of info in here for Air to Ground attacks too, essential if you're bombing!
http://mywebpages.comcast.net/Tailspin/index.htm
If you want to get seriously technical, then have a look here. You can read up about everything to do specifically with ONLINE sim flying, something a lot of other sites don't mention.
http://www.simhq.com/_air/acc_library.html
A very nice site covering Soviet fighter tactics, with some great animations to explain the theories. Plenty of comparison with German aircraft too, so you can learn how to fight to your strengths and your opponent's weakness.
http://luthier.stormloader.com/home.html
Another great IL2 specific site but with some great Realplayer video showing the manouvers and when to use them. Gives you views from each plane's cockpit as well.
http://magnum-pc.netfirms.com/mudmov...actics_bfm.htm
More fighter tactics, based on jets, but again very handy to know and well worth a read.
http://www.sci.fi/~fta/acmintro.htm
Other sites
Netwings, not just another forum, but one that is populated almost entirely by flight sim enthusiasts.
http://www.netwings.org/cgi-bin/dcforum/dcboard.cgi